A Multi-Input Multi-Output (MIMO) technology greatly increases the system throughput and the transmission distance without increasing bandwidth or total transmitting power, and is being used widely in the wireless communication field.
To achieve the capacity supported by the MIMO and the maximum gain of performance, a precoding method or an FDE method may be applied to suppress channel interference and distortion and improve the Bit Error Ratio (BER) performance, that is, reduce the bit error ratio.
The current precoding method is categorized into linear precoding and nonlinear precoding.
Linear precoding, such as, Zero Forcing (ZF) precoding and Minimum Mean Square Error (MMSE) precoding.
Nonlinear precoding, such as, Dirty Paper Coding (DPC) and Tomlinson-Harashima Precoding (THP).
FDE method, such as, Single-Carrier Frequency Domain Equalization (SC-FDE) applicable to Single-carrier Frequency-Division Multiple Access (SC-FDMA).
In the existing linear precoding, a linear combination of code sources of different transmitting antennas is multiplied by a precoding matrix of the signal vector. In this way, each receiving antenna can receive interference-free signals, the complexity of calculation is low, but the BER is high.
Although the existing nonlinear precoding reduces the BER, referring to Table 1, supposing that the number of transmitting antennas is N and the number of receiving antennas is N, the complexity of the nonlinear precoding is much higher than the complexity of linear precoding. Especially, the complexity of DPC is very high, as much as eN, which makes the implementation rather difficult.
TABLE 1Precoding methodMMSETHPDPCComplexity6N3 + 4N2 − 2N + 3      4    ⁡          [              N        +                  2          ⁢                      (                          N              -              1                        )                          +                  3          ⁢                      (                          N              -              2                        )                          +        …        +                              N            2                    ⁢                      (                                          N                2                            +              1                        )                              ]        +      6    ⁢          N      3        +            13      2        ⁢          N      2        -            9      2        ⁢    N    +  6O(eN)
The existing frequency equalization method generally takes linear equalization as mainstream, and therefore, defects that calculation complexity is low while BER is high exist.